Well, I finally got around to checking my brake lines as suggested by Clockwork! It took me more than 6 months to get around to it.

Incredibly, all the lines were clean and rust-free.

All I had to do was unscrew the 10mm screws from the long plastic sill cover running from the LHS front wheel arch to the LHS rear wheel arch (no need to remove all those plastic one-use rivets from the edge), then pry the cover down about 2-3 inches from the inboard side. This allows a fairly clear view of all the fuel lines and junctions.